CN117981017A

CN117981017A - Electroactive fiber

Info

Publication number: CN117981017A
Application number: CN202280064199.7A
Authority: CN
Inventors: T·金; J-W·全
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2021-09-24
Filing date: 2022-09-21
Publication date: 2024-05-03
Also published as: WO2023046781A1; EP4156208A1; KR20240066175A

Abstract

The invention relates to a method (1) for manufacturing a fluoropolymer coated wire, comprising: -a step (2) of providing a solution of the metal wire and at least one fluoropolymer in a solvent, wherein the fluoropolymer has a proportion of less than 10% by weight and 1% by weight or more relative to the total weight of the solution; -a step (3) of dip-coating the metal wire in a first solution of fluoropolymer to deposit a first layer of the solution of fluoropolymer at the surface of the metal wire; and-a step (4) of drying to evaporate the solvent from the deposited first layer and form a first layer of fluoropolymer at the surface of the metal wire.

Description

Electroactive fiber

Technical Field

The present invention relates to the field of electroactive textiles (textiles). More particularly, the present invention relates to a method for manufacturing an electroactive fiber comprising at least one fluoropolymer shell adhered to a metal core.

Background

As the demand for internet of things (IoT) and system on chip (SoC) technologies has grown rapidly, so has the demand for wearable sensors and devices. Among the many possible solutions, the development of electroactive fibers is expected to be a critical solution that can meet the needs of intelligent textile technology.

Ferroelectric and relaxor ferroelectric materials that produce mechanical effects caused by external electric fields have attracted considerable attention and have been approved for use in a variety of transducer, actuator and sensor applications.

Among piezoelectric materials, ceramics are the most commonly used materials due to their good actuation properties and their very wide bandwidth. However, they are brittle, which makes them impossible to apply to curved or complex surfaces.

Other conductive devices use a polymer film sandwiched between two electrodes. Among the polymers that can be used, in particular fluoropolymers based on vinylidene fluoride (VDF), represent a class of compounds that have remarkable properties for a large number of applications. Polyvinylidene fluoride (PVDF) and copolymers including VDF and trifluoroethylene (TrFE) are of particular interest due to their piezoelectric properties.

As mentioned in publication "Polymeric piezoelectric fiber with metal core produced by electrowetting-aided dry spinning method."J.Appl.Polym.Sci.133,n/a-n/a(2016) of Liu, w., chen, r., ruan, x, and Fu, x, it is known to use a metal core (e.g., made of stainless steel) coated with a piezoelectrically active polymer provided by extrusion, a technique known as stretch-melt coating. This technique has proven to be difficult to implement and has drawbacks. It requires polymers with low melt viscosity and results in considerable coating thickness: although this publication states that thicknesses greater than 20 μm can be obtained, the thicknesses generally obtained by this technique are much higher, equal to about 100 μm or more. A first disadvantage of this technique is that excessive polymer thickness requires the application of high bias voltages, which can be problematic because it results in air breakdown or requires complex equipment. Furthermore, excessive polymer thickness typically causes a nonlinear response of the piezoelectric polymer. A second disadvantage of this technique is that centering the metal core in the polymer coating is complicated, the smaller the desired thickness, the more difficult the problem is to control.

The use of solvent-based coating methods makes it possible to overcome the melt viscosity problem and to easily obtain fluoropolymer coatings of lower thickness, typically between 1 and 40 μm, smaller than 100 μm. The main challenge of solvent-based coating techniques is to create a tacky and uniform fluoropolymer layer at the surface of the wire.

The publication Liu, w. already mentioned above describes an electrowetting-assisted solvent based coating of PVDF or P (VDF-TrFE) copolymer on a metal core. 100 μm diameter copper wire (6 μm thick) of polyester-imide enamels (enamelled) was used as the core of the center. PVDF (mw=5,340 g/mol) and P (VDF-TrFE) (VDF/TrFE mass ratio: 70/30) copolymers in powder form were dissolved in 1/1 dimethylformamide/acetone mixture at concentrations of 10 wt%, 15 wt% and 20 wt%. The enamelled wire is passed through a polymer solution, then through a copper needle of 1mm diameter and finally through a series of concentric electrodes of 3.5mm to 0.5 mm. The coating nozzle was biased at 1 kV. The copper core stripped of its enamel is grounded and the electrode is connected to a continuous high voltage of 4 kV. The applied electric field is less than 20MV/m. Crystallization of the polymer is carried out by solvent evaporation. The obtained fibers were metallized with gold by cathode sputtering. The authors showed that the use of the electrowetting method makes it possible to obtain a more uniform, smoother and more viscous electroactive polymer layer on the enamelled copper than without high voltage. Most of the solutions used gave coating thicknesses of between 3 and 8 μm. Thickness uniformity is improved by using high voltages.

A highly uniform thickness of the electroactive coating is desirable because it enables more reliable electroactive fibers to be obtained, which are particularly less prone to shorting. However, the electrowetting-assisted solvent-based coating method is still quite complex to use, as it involves high voltages during manufacture and requires the use of enamelled copper wires.

Patent document WO 2020/128230 describes solvent-based coatings of P (VDF-TrFE) copolymers without the use of electrowetting-assisted techniques. Bare metal wires (non-coated metal wires) were coated with a formulation comprising 10 to 30 wt% of a fluoropolymer in solvent P (VDF-TrFE) copolymer solution, surfactant and adhesion promoter. Although this technique has proven to be effective and easier to implement than the electrowetting-assisted technique, it requires the use of additives that ultimately remain in the coating.

Thus, there is a need to further develop a simpler and reliable solvent-based coating method that is capable of obtaining a uniform coating of fluoropolymer at the surface of the metal wire.

Purpose(s)

It is an object of the present invention to at least partially overcome the disadvantages of the prior art.

One object of the present invention is in particular to propose a solvent-based coating method which enables a thin uniform coating of fluoropolymer to be obtained at the surface of the metal wire.

According to at least some embodiments, it is an object of the present invention to propose a simple and/or inexpensive and/or high-yield and/or highly reliable solvent-based coating process.

According to at least some embodiments, it is also an object of the present invention to propose high quality electroactive fibers and textiles made therefrom. The fibers may have a smooth outer surface and exhibit good adhesion of the metal-fluoropolymer coating to avoid shorting and obtain a reliable sensor thereof. This may have important uses in smart textiles.

Disclosure of Invention

The present invention relates to a method for manufacturing a fluoropolymer coated wire comprising:

-a step of providing a solution of the metal wire and at least one fluoropolymer in a solvent, wherein the fluoropolymer has a proportion of less than 10% by weight and 1% by weight or more relative to the total weight of the solution;

-a step of dip-coating the metal wire in a first solution of fluoropolymer to deposit a first layer of the solution of fluoropolymer at the surface of the metal wire; and

A step of drying to evaporate the solvent from the deposited first layer and form a first layer of fluoropolymer at the surface of the metal wire.

The inventors have noted that working at low concentration of fluoropolymer in solution enables highly uniform fluoropolymer layers to be obtained without any electrowetting technique and/or without the use of any wetting agent and/or adhesion promoter.

The method may further comprise one or more optional subsequent steps of dip coating and drying, respectively, to add further layers of fluoropolymer, the solvent and the proportion of fluoropolymer in solution for the subsequent dip coating steps being independently selected.

According to a preferred embodiment, the fluoropolymer may preferably have a proportion of fluoropolymer of 9% by weight or less and 3% by weight or more, more preferably 8% by weight or less and 5% by weight or more, relative to the total weight of the solution.

In some embodiments, the fluoropolymer may be a copolymer comprising at least 80 mole percent of units derived from vinylidene fluoride (VDF) and from trifluoroethylene (TrFE),

Wherein the proportion of units derived from TrFE ranges from 5 to 95 mole%, and preferably from 15 to 55 mole%, relative to the sum of units derived from VDF and derived from TrFE.

In some embodiments, the fluoropolymer may be a terpolymer of P (VDF-TrFE-X) consisting of:

-50 to 80 mole% of units obtained from VDF;

15 to 40 mole% of units derived from TrFE, and

-1 To 15 mole% of units obtained from a third monomer X.

The third monomer may preferably be selected from the list consisting of: trifluoroethylene, hexafluoroethylene, trifluoropropene, tetrafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene. The third monomer may more preferably be chlorotrifluoroethylene or chlorotrifluoropropylene.

In some other embodiments, the fluoropolymer may be a copolymer consisting essentially of or consisting of units derived from VDF and TrFE, wherein the proportion of units derived from TrFE ranges from 15 to 55 mole%, preferably from 16 to 45 mole%, more preferably from 17 to 35 mole%, and most preferably from 18 to 28 mole%, relative to the sum of units derived from VDF and TrFE.

In some embodiments, the solvent may be selected from the list of:

ketones, in particular methyl isobutyl ketone, methyl ethyl ketone, cyclopentanone and acetone,

Esters, in particular ethyl acetate, methyl acetate, propyl acetate, butyl acetate and propylene glycol methyl ether acetate,

Amides, such as dimethylformamide and dimethylacetamide,

-A solvent of dimethyl sulfoxide and a solvent of dimethyl sulfoxide,

Furan, in particular tetrahydrofuran,

The presence of carbonates, in particular dimethyl carbonate,

Phosphate esters, in particular triethyl phosphate,

-And mixtures thereof

The solvent may be chosen in particular from the list: methyl ethyl ketone, cyclopentanone, dimethyl sulfoxide, and mixtures thereof.

In some preferred embodiments, the solution may be free of any surfactant and/or may be free of any adhesion promoter.

In some embodiments, the solution may be comprised of a fluoropolymer and a solvent.

In some embodiments, the method may include 1 to 100, preferably 3 to 50, and more preferably 5 to 20, subsequent steps of dip coating and drying.

In some preferred embodiments, the fluoropolymer coating has an average thickness at the surface of the metal wire of 0.1 to 100 microns, preferably 0.5 to 50 microns, and more preferably 1 to 40 microns.

The invention also relates to a wire obtained by the method of the invention and a piezoelectric fabric comprising at least one wire obtained by said method.

Drawings

Fig. 1 shows a block diagram of a method according to the invention.

Fig. 2 shows a schematic diagram of a spinning apparatus suitable for carrying out the method of the invention.

Fig. 3 and 4 are photomicrographs of the coated cable prepared in example 1. Fig. 3 shows an external aspect (appearance), while fig. 4 is a cross-sectional view.

Fig. 5 is a microscopic view of the external aspect of the coated cable prepared in comparative example 1.

Fig. 6 shows different configurations in a textile of an electroactive transducer.

Fig. 7 shows a woven textile with two sensing areas made with the coated fibers of example 1.

Fig. 8 shows waveforms after drop sensing test (drop SENSING TEST). By "reverse circuit" is meant a reverse connection to the oscilloscope compared to the "forward circuit".

Detailed Description

Fluorine-containing polymer

Fluoropolymers are polymers having a carbon chain that includes structural units (or units, or repeating units, or portions) that include at least one fluorine atom.

Preferably, the fluoropolymers may comprise units derived from vinylidene fluoride (VDF) monomers (i.e. they are obtained by polymerization of vinylidene fluoride (VDF) monomers).

The fluoropolymer may be a PVDF homopolymer. Preferably, however, the fluoropolymer may be a copolymer (in a broad sense), which means that it comprises units derived from at least one monomer X other than VDF. Depending on the case, a single monomer X, or a plurality of different monomers X, may be used.

In some embodiments, monomer X may be of formula CX ₁X₂＝CX₃X₄, wherein each group X ₁、X₂、X₃ and X ₄ is independently selected from H, cl, F, br, I and optionally partially or fully halogenated C1-C3 (preferably C1-C2) alkyl groups—this monomer X is different from VDF (i.e., if X ₁ and X ₂ represent H, at least one of X ₃ and X ₄ does not represent F, and if X ₁ and X ₂ represent F, at least one of X ₃ and X ₄ does not represent H).

In some embodiments, each of the groups X ₁、X₂、X₃ and X ₄ may independently represent a H, F, cl, I or Br atom, or a methyl group optionally including one or more substituents selected from F, cl, I, and Br. In particular, in some embodiments, each group X ₁、X₂、X₃ and X ₄ may independently represent H, F, cl, I or Br atoms.

In some embodiments, only one of X ₁、X₂、X₃ and X ₄ may represent a Cl or I or Br atom, and the other of the groups X ₁、X₂、X₃ and X ₄ may independently represent: an H or F atom, or a C1-C3 alkyl group optionally including one or more fluoro substituents; preferably, an H or F atom, or a C1-C2 alkyl group optionally including one or more fluoro substituents; and more preferably a H or F atom, or a methyl group optionally including one or more fluoro substituents.

Examples of monomers X are as follows: vinyl Fluoride (VF), trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), trifluoropropene, and in particular 3, 3-trifluoropropene, tetrafluoropropene, and in particular 2, 3-tetrafluoropropene or 1, 3-tetrafluoropropene (in cis or preferably trans), hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, and in particular 1, 3-pentafluoropropene or 1,2, 3-pentafluoropropene, perfluoroalkyl vinyl ethers, and in particular those of the general formula Rf-O-cf=cf2, rf being an alkyl group, preferably a C1 to C4 alkyl group (preferred examples being perfluoropropyl vinyl ether or PPVE, and perfluoromethyl vinyl ether or PMVE).

In some embodiments, monomer X may include a chlorine or bromine atom. It may be chosen in particular from bromotrifluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene. The chlorofluoroethylene may represent 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. Preference is given to the 1-chloro-1-fluoroethylene isomer (CFE). The chlorotrifluoropropene is preferably 1-chloro-3, 3-trifluoropropene (in cis or trans, preferably trans form) or 2-chloro-3, 3-trifluoropropene.

In some embodiments, the fluoropolymer may comprise units derived from VDF and HFP, or may be a P (VDF-HFP) polymer composed of units derived from VDF and HFP. The molar proportion of the repeating units obtained from HFP may preferably be 2% to 50%, particularly 5% to 40%.

In some preferred embodiments, the fluoropolymer may comprise units derived from VDF and CFE, or from CTFE, or from TFE, or from TrFE. The molar proportion of repeating units obtained from monomers other than VDF may preferably be less than 50%, more preferably less than 40%.

In some preferred embodiments, the fluoropolymer may be a copolymer (broadly) comprising at least 80 mole% of units derived from VDF and TrFE.

The proportion of the units obtained from TrFE may preferably be 5 to 95 mol% with respect to the sum of the units obtained from VDF and TrFE, and in particular: 5 to 10 mole% or 10 to 15 mole%; or 15 to 20 mole%; or 20 to 25 mole%; or 25 to 30 mole%; or 30 to 35 mole%; or 35 to 40 mole%; or 40 to 45 mole%; or 45 to 50 mole%; or 50 to 55 mole%; or 55 to 60 mole%; or 60 to 65 mole%; or 65 to 70 mole%; or 70 to 75 mole%; or 75 to 80 mole%; or 80 to 85 mole%; or 85 to 90 mole%; or 90 to 95 mole%. Particularly preferably in the range of 15 to 55 mol%.

In some preferred embodiments, the fluoropolymer may be a terpolymer consisting of units derived from VDF, trFE and another monomer X different from VDF and TrFE as defined above, or a P (VDF-TrFE-X) polymer consisting of units derived from VDF, trFE and another monomer X. In this case, preferably, the further monomer X may be selected from TFE, HFP, trifluoropropene, and in particular 3, 3-trifluoropropene, tetrafluoropropene, and in particular 2, 3-tetrafluoropropene or 1, 3-tetrafluoropropene (in cis or preferably trans), bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene. Monomers CTFE or CFE are particularly preferred. The proportion of units (relative to the total amount of units) obtained from the further monomer X in the fluoropolymer may range, for example, from 1 to 2 mol%; or 2 to 3 mole%; or 3 to 4 mole%; or 4 to 5 mole%; or 5 to 6 mole%; or 6 to 7 mole%; or 7 to 8 mole%; or 8 to 9 mole%; or 9 to 10 mole%; or 10 to 12 mole%; or 12 to 15 mole%; or 15 to 20 mole%. A range of 1 to 15 mole% is particularly suitable.

In some preferred embodiments, the fluoropolymer may be a terpolymer of P (VDF-TrFE-X), such as P (VDF-TrFE-CFE) or P (VDF-TrFE-CTFE), and may consist of:

-50 to 80% of the units obtained from VDF;

15 to 40% of units obtained from TrFE, and

-2 To 15% of units obtained from a third monomer.

In some preferred embodiments, the terpolymer of P (VDF-TrFE-X), in particular P (VDF-TrFE-CFE), may consist of:

60 to 70% of the units obtained from VDF,

25 To 35% of units obtained from TrFE,

-2.5 To 10% of units obtained from a third monomer.

In some other embodiments, the fluoropolymer may consist essentially of units derived from VDF and TrFE, meaning that it contains less than 2 mole% of units derived from any additional monomer, and may preferably consist of VDF and TrFE.

In some preferred embodiments, the fluoropolymer may be a copolymer composed of units derived from vinylidene fluoride and units derived from trifluoroethylene, or P (VDF-TrFE). The proportion of the units derived from TrFE may preferably be 5 mol% to 95 mol% with respect to the sum of the units derived from VDF and TrFE, and in particular: 5 to 10 mole%; or 10 to 15 mole%; or 15 to 20 mole%; or 20 to 25 mole%; or 25 to 30 mole%; or 30 to 35 mole%; or 35 to 40 mole%; or 40 to 45 mole%; or 45 to 50 mole%; or 50 to 55 mole%; or 55 to 60 mole%; 10 or 60 to 65 mole%; or 65 to 70 mole%; or 70 to 75 mole%; or 75 to 80 mole%; or 80 to 85 mole%; or 85 to 90 mole%; or 90 to 95 mole%. Particularly preferably in the range of 15 to 55 mol%.

In some preferred embodiments, the proportion of units derived from TrFE obtained from TrFE may range from 15 to 55 mole%, preferably from 16 to 45 mole%, more preferably from 17 to 35 mole%, and most preferably from 18 to 28 mole%, relative to the sum of units derived from VDF and from TrFE.

In some embodiments, the curie temperature (Curie temperature) of the fluoropolymer or P (VDF-TrFE) copolymer consisting essentially of units derived from VDF and TrFE can be between 50 ℃ and 145 ℃. Curie temperature can be measured by differential scanning calorimetry or by dielectric spectroscopy.

The fluoropolymers used in the process of the present invention may be prepared by using any known method, such as emulsion, microemulsion, suspension and solution polymerization

The molar composition of the units in the fluoropolymer can be determined by various means such as infrared spectroscopy or raman spectroscopy. Conventional elemental analysis methods of carbon, fluorine and chlorine, or bromine, or iodine elements, such as X-ray fluorescence spectroscopy, allow the mass composition of the polymer to be calculated, from which the molar composition is deduced. Polynuclear NMR techniques, particularly proton (1H) and fluorine (19F) NMR techniques, can also be used to analyze solutions of the polymer in suitable deuterated solvents. Finally, elemental analysis, for example for heteroatoms such as chlorine or bromine or iodine, can be combined with NMR analysis. Thus, the content of units derived from CTFE in a P (VDF-TrFE-CTFE) terpolymer can be determined, for example, by measuring the content of chlorine via elemental analysis.

Fluoropolymers, particularly P (VDF-TrFE) copolymers and P (VDF-TrFE-CFE) and P (VDF-TrFE-CTFE) terpolymers, may preferably be random and linear. They may be homogeneous or heterogeneous. Homogeneous polymers have a uniform chain structure with little variation in the random distribution of units derived from the various monomers between the chains. In heterogeneous polymers, the chains have a distribution of units derived from various monomers, either multimodal or spread-out. Thus, a heterogeneous polymer comprises chains that are more enriched in (in) a given unit and chains that are less enriched in (in) a given unit.

According to some embodiments, the weight average molar mass of the fluoropolymer, and in particular the P (VDF-TrFE) copolymer, and the P (VDF-TrFE-CFE), and the P (VDF-TrFE-CTFE) terpolymer, may range from 150 to 2000 g/mol, preferably from 250 to 1 500 g/mol, and more particularly from 300 to 800 g/mol. In the context of the present patent application, the weight average molar mass is also referred to as the "molecular weight" (Mw) of the fluoropolymer. The latter can be adjusted by changing some parameters of the fluoropolymer manufacturing process, such as the temperature in the reactor or by adding transfer agent.

The molecular weight distribution can be estimated by SEC (size exclusion chromatography) using Dimethylformamide (DMF) as eluent, with a set of three columns of increasing porosity. The stationary phase is styrene-DVB gel. The detection process is based on refractive index measurements and is calibrated using polystyrene standards. The sample was dissolved in DMF at 0.5g/l and filtered through a 0.45 μm nylon filter.

Solution of fluoropolymer in solvent

Fluoropolymers such as P (VDF-TrFE) copolymers, or P (VDF-TrFE-CFE) or P (VDF-TrFE-CTFE) terpolymers are dissolved in a solvent to form a solution at 1 wt% or more to 10 wt% (excluding), the percentages being given by weight of the fluoropolymer relative to the total weight of the solution. The inventors have noted that even layers of fluoropolymer may not be obtained above 10 wt.% without supplemental techniques including electrowetting and/or formulating the composition with wetting agents and/or adhesion promoters.

Surprisingly, in the range of 1 to 10 wt%, a uniform layer can be obtained even without using the previously cited techniques. Below 1 wt%, the solution may become too fluid to obtain the desired fluoropolymer layer.

In some embodiments, the concentration of fluoropolymer in the solution is 9.5 wt% or less, or 9 wt% or less, or 8.5 wt% or less, or 8 wt% or less.

In some embodiments, the concentration of fluoropolymer in the solution is greater than 1 wt%, or 2 wt% or greater, or 3 wt% or greater, or 4 wt% or greater, or 5 wt% or greater.

In some embodiments, the concentration of the fluoropolymer may be 1 wt% to 2 wt%, or 2 wt% to 3 wt%, or 3 wt% to 4 wt%, or 4 wt% to 5 wt%, or 5 wt% to 6 wt%, or 6 wt% to 7 wt%, or 7 wt% to 8 wt%, or 8 wt% to 9 wt%, or 9 wt% to less than 10 wt%.

Preferably, the concentration of fluoropolymer is 3 to 9% by weight.

More preferably, the concentration of fluoropolymer is from 5 to 8 weight percent.

According to one embodiment, the solvent may be selected from the list of:

Ketones, in particular methyl isobutyl ketone, methyl Ethyl Ketone (MEK), cyclopentanone and acetone,

Amides such as dimethylformamide and dimethylacetamide,

-A solvent of dimethyl sulfoxide and a solvent of dimethyl sulfoxide,

Furan, in particular tetrahydrofuran,

The presence of carbonates, in particular dimethyl carbonate,

Phosphate esters, in particular triethyl phosphate,

-And mixtures thereof

Preferably, the solvent may be selected from: methyl ethyl ketone, cyclopentanone, dimethyl sulfoxide, and mixtures thereof.

According to some embodiments, the solution may be free of any surfactant and/or may be free of any adhesion promoter.

Surfactants are chemicals that are added to ensure better wetting of the fluoropolymer solution on the metal wire. As mentioned in WO 2020/128230, the solution may in particular be free of any surfactant based on acrylic copolymers (e.g. BYK 3440) or on high molecular weight block acrylic copolymers (e.g. Disperbyk 163).

Adhesion promoters are chemicals that enhance fluoropolymer-metal adhesion. The solution may in particular be free of any adhesion promoters based on functional copolymers of the hydroxyl type with acid groups (for example BYK 4510) or adhesives of the ethoxysilane type, for example 3-aminopropyl triethoxysilane (DYNASYLAN AMEO).

According to a preferred embodiment, the solution may consist of a fluoropolymer and a solvent.

According to a preferred embodiment, the viscosity of the solution may advantageously be between 0.015 and 1pa.s for a shear rate of 10s ^-1. The viscosity was measured at ambient temperature of 25℃using a Brookfield viscometer according to standard ASTM D2983-20. This viscosity range enables the formation of a thin, substantially uniform layer of the fluoropolymer solution at the surface of the wire. Preferably, the viscosity of the solution may be 0.02 to 0.5pa.s. The viscosity of the dip coating solution may in particular be from 0.020 to 0.025pa.s, or from 0.025 to 0.05pa.s, or from 0.05 to 0.075pa.s, or from 0.075 to 0.1pa.s, or from 0.1 to 0.2pa.s, or from 0.2 to 0.3pa.s, or from 0.3 to 0.4pa.s, or from 0.4pa.s to 0.5pa.s.

Method for manufacturing fluoropolymer coated wire

The present invention relates to a solvent-based process for continuously manufacturing fluoropolymer coated metal wire forming electroactive fibers. Such electroactive fibers may be of particular interest for smart textiles. Fig. 1 is a block diagram of a method 1 describing the various steps of the method according to the invention. Fig. 2 shows a schematic view of one particular spinning apparatus 10 in which the method may be performed.

Referring to fig. 1, method 1 includes step 2: a solution of a metal wire and one or more fluoropolymers in a solvent is provided.

The metal may preferably have a conductivity of greater than 0.5MS/m and may be selected from the list of: copper, platinum, stainless steel, molybdenum. The wire may be single-stranded or multi-stranded with an outer diameter in the range of 50 to 900 μm, and preferably 80 to 300 μm. The metal may have a Young's modulus greater than 1GPa and an elastic elongation between 1% and 10%. Advantageously, the wire may be degreased in a tank (not shown) using alkaline, acidic or detergent solutions or with alcohols before being coated.

Solutions of one or more fluoropolymers in a solvent as described above are provided. Multiple solutions with different fluoropolymers and/or different solvents and/or different proportions of fluoropolymers in the solvents may be prepared, as the fluoropolymer coating may be prepared by depositing multiple fluoropolymer layers (see optional steps 5 and 6 below).

In some embodiments, several solutions may in particular consist of the same fluoropolymer and the same solvent, but with different proportions of fluoropolymer in the solution.

In some embodiments, only one solution may be provided and used to deposit multiple layers.

The method 1 further comprises the step 3: dip-coating the metal wire in a (first) solution of the fluoropolymer to deposit a (first) layer of the solution of the fluoropolymer at the surface of the metal wire. Referring to fig. 2, bare wire 11 may be unwound from a roll 12 and guided by a guide roll 15 to a bath 13 of (first) solution 14 containing fluoropolymer. The wire passes through and out of the bath and a (first) layer of the solution of the fluoropolymer is deposited at the surface of the wire 15.

The temperature of the fluoropolymer solution in the bath may be below the boiling temperature of the solvent. Preferably, the temperature of the solution of fluoropolymer is less than 80 ℃, or less than 70 ℃, or less than 60 ℃, or less than 50 ℃, or less than 40 ℃. In some preferred embodiments, the solution of fluoropolymer is at ambient temperature in the bath, i.e., typically between 10 ℃ and 30 ℃.

The method 1 further comprises a step 4 of drying to evaporate the solvent from the deposited (first) layer. The drying process may include passing the coated wire through a passage 17 of hot air blown at a temperature below the melting temperature of the fluoropolymer so that the solvent of the deposited layer of fluoropolymer solution may be evaporated. The drying temperature, in particular for the P (VDF-TrFE) copolymer, the P (VDF-TrFE-CFE) and the P (VDF-TrFE-CTFE) terpolymer, can be, for example, between 50℃and 150 ℃. Alternative or complementary drying methods known to those skilled in the art, such as the use of infrared radiation, may also be used. The wire exits the passage of hot air and is coated with a (first) dried layer of fluoropolymer at the surface of the metal wire 18.

The (first) deposited layer of fluoropolymer generally has an average thickness of 0.1 to 10 μm, preferably 0.5 to 7 μm, and most preferably 1 to 5 μm. Due to scanning electron microscopy, the average thickness can be estimated by directly measuring the cross section of the coated wire. The image may be binarized and analyzed to determine a minimum thickness, a maximum thickness, and an average thickness of the cross section.

The layer thickness of the deposited layer is highly uniform. Uniformity can be assessed due to the R ratio defined as follows:

R＝(r_{Maximum value}-r_{Minimum of})/r_{Maximum value}，

Where r _{Maximum value} is the highest thickness when measured in cross section and r _{Minimum of} is the lowest thickness when measured in cross section.

The R ratio may preferably be less than 0.30, more preferably less than 0.25, even more preferably less than 0.20, and most preferably less than 0.15.

The calculated R ratio can be obtained by one measurement of a single cross section. Preferably, the R ratio is obtained by using the highest value of R _{Maximum value} and the lowest value of R _{Minimum of} measured over several cross sections, e.g. at least 5 cross sections or at least 10 cross sections separated by a distance of e.g. 1cm, or 10cm, or 1 meter. In some embodiments, the R ratio may be obtained by using the highest value of R _{Maximum value} and the lowest value of R _{Minimum of} for 5 cross sections separated by a distance of about 1 cm.

Optionally, the method 1 may further comprise n subsequent dip coating steps 5 and drying step 6, wherein n further layers are added in the same manner as the first layer of fluoropolymer. These n subsequent steps allow for adjustment of the thickness of the final fluoropolymer coating.

The number n may be from 1 to 100, preferably from 3 to 50, and more preferably from 5 to 20. As a result, the average thickness of the fluoropolymer coating at the surface of the metal wire may be 0.1 to 100 microns, preferably 0.5 to 50 microns, and more preferably 1 to 40 microns. The average thickness of the fluoropolymer coating may be in particular 1 to 10 micrometers, or 10 to 20 micrometers, or 20 to 30 micrometers, or 30 to 40 micrometers.

In some embodiments, the solution used to deposit the first layer is more dilute than the solution used to deposit the last layer.

The method 1 may finally comprise a step 7 of winding the coated wire. The coated wire may be conveyed along several Godet rolls (Godet rolls) 16 (heatable rolls) to complete the drying step and put the wire under tension.

Electroactive transducer

In a piezoelectric composite fiber comprising a metal wire covered by a fluoropolymer coating, the metal wire acts as an internal electrode.

Some uses of such composite piezoelectric fibers require deposition of an outer electrode on the fluoropolymer coating.

In some embodiments, the fluoropolymer coated wire may be further continuously covered by a counter electrode according to one of the following approaches:

solvent-based coating with a solution of a conductive polymer, for example PEDOT: PSS (PEDOT stands for poly (3, 4-ethylenedioxythiophene) and PSS stands for poly (styrenesulfonate)) in a bath (dipping) or in a coating nozzle; or (b)

-Liquid-based coating by dipping or in a coating nozzle using a conductive ink of the silver-based paint or carbon varnish type (carbon or nano-carbon black); or (b)

-Melt route coating with CPC polymer; in this case, without stretching and without alignment of the filler, the conductivity is greater than 100S/m; or (b)

-Metallizing by evaporating gold or another conductive metal; or (b)

-Bonding a conductive metal wire around the piezoelectrically active coating; or (b)

Braiding metal wires (ropes, cables, etc.) around the piezoelectrically active coating.

However, in some other embodiments, the fluoropolymer coated wire may not need to be covered with a counter electrode. Indeed, as shown below, in piezoelectric fabrics, the effect on the electrodes can be exerted by other pure conductive fibers or by fibers coated with fluoropolymers.

Textile product

The fluoropolymer coated fibers may be woven together and/or with other pure conductive fibers (without fluoropolymer coating), such as bare metal wires, in order to obtain a textile exhibiting an interlocking network of piezoelectric sensors and/or actuators. The textile product obtained by the weaving method may consist of warp yarns and weft yarns.

Each transducer, sensor and/or actuator is composed of one or more piezoelectric coatings between two electrodes. Several possible configurations are presented in fig. 6:

a) Weaving one fluoropolymer coated fiber 20 so that it is substantially parallel to the other conductive fiber 21 (without fluoropolymer coating);

B) Two fluoropolymer coated fibers are woven substantially parallel to each other;

C) Two fluoropolymer coated fibers were woven substantially perpendicular to each other;

d) One fluoropolymer coated fiber was woven so that it was significantly perpendicular to the other conductive fiber (without fluoropolymer coating).

Annealing step

Once the wire has been coated with a fluoropolymer coating, such as when fluoropolymer coated fibers have been woven into a textile, thermal annealing steps known to those skilled in the art may allow and/or increase crystallization of the fluoropolymer to improve piezoelectric properties.

The thermal annealing step preferably lasts 12 hours or less, more preferably 6 hours or less, even more preferably 1 hour or less, even more preferably 30 minutes or less, and most preferably 15 minutes or less.

Bias step

The operation includes applying an electric field between the surface of the adhered polymer layer and the central metal core. In embodiments in which the coated fiber does not contain any counter electrode, two methods known to those skilled in the art may be employed: direct contact bias and non-contact bias. In embodiments in which the counter electrode has been deposited on the coated fiber, the biasing may be performed in-line.

Examples

The examples which follow illustrate the invention.

Example 1

A solution containing 8% by weight of a P (VDF-TrFE) (80/20 mol%) copolymer (having a molecular weight Mw of 630.000 g/mol) was prepared by dissolution in polypropylene glycol monomethyl ether acetate with stirring at 60 ℃.

The solution had a viscosity of 0.24Pa.S at 25℃for a shear rate of 10s ^-1 using a Brookfield viscometer according to standard ASTM D2983-20. The P (VDF-TrFE) solution does not contain any other additives.

According to the method of the present invention ten successive steps of dip coating in the solution prepared above and drying are used to produce a coated fiber of stranded copper wire having a diameter of about 181 μm.

The winding speed of the winding roller was 5 m/min. The drying step was performed by blowing hot air at a temperature of 145 ℃.

The obtained P (VDF-TrFE) had an average thickness of 30 μm (maximum thickness: 34 μm; minimum thickness: 26 μm) when measured by a microscope on a cross section (see FIGS. 3 and 4).

Comparative example 1

A solution containing 15% by weight of P (VDF-TrFE) (70/30 mol%) copolymer (having a molecular weight Mw of 600.000 g/mol) was prepared by dissolution in N, N dimethylformamide.

A layer of fluoropolymer was coated on the surface of the same stranded copper wire used in example 1 using the same method as described in example 1. The resulting fibers exhibited a very non-uniform fluoropolymer layer (see fig. 5).

Comparative example 2

A solution containing 15% by weight of a P (VDF-TrFE) (80/20 mol%) copolymer (having a molecular weight Mw of 630.000 g/mol) was prepared by dissolution in polypropylene glycol monomethyl ether acetate with stirring at 60 ℃.

A layer of fluoropolymer was coated on the surface of the same stranded copper wire used in example 1 using the same method as described in example 1. The resulting fibers exhibited a non-uniform fluoropolymer layer, such as that observed in comparative example 1.

Manufacture of smart textiles

Three textiles were woven: one comprising the fiber prepared according to example 1 (see photograph on fig. 7; see also fig. 6-C), one comprising the fiber prepared according to comparative example 1, and one comprising the fiber prepared according to comparative example 2. The textile is made of four fluoropolymer coated fibers used as warp yarns and sixteen (8 x 2) fluoropolymer coated fibers used as weft yarns to obtain two sensing areas.

The textile was then annealed by heating it at a temperature of 140 ℃ for 10 minutes. Finally, the annealed textile was biased at room temperature (23 ℃) by contact polarization at a voltage of 100V/μm (the total thickness of the fluoropolymer coating between the two electrodes was calculated).

Characterization of textiles

Drop-sensing tests were performed on each fabric. Weft and warp fibers from one sensing region were connected on a 2-channel oscilloscope ("forward circuit"). A weight of 0.25kg was dropped from a height of 3cm onto the attached sensing area. The reverse connection is referred to herein as the "reverse circuit".

Textiles prepared with the fibers prepared according to comparative example 1 or comparative example 2 showed that a portion of the fluoropolymer coating was torn after polarizing the fibers. Which does not respond to drop sensing testing, possibly due to a short circuit in the structure.

The textile product prepared with the fiber according to example 1 is highly responsive to falling of weights thereon (see fig. 8).

THE ADVANTAGES OF THE PRESENT INVENTION

The invention presents one or more of the following advantages:

the process is easy to carry out, requires little investment in equipment (bath, drying, wet spinning, winding);

The process is easy to adapt to different production scales from laboratory to pilot plant and finally to mass production: it depends mainly on bath size and wire length;

The method enables to obtain fluoropolymer coated wires with high reliability: the uniformly applied fluoropolymer coating enables continuous manufacture with high productivity;

The textile product made from the fluoropolymer yarn made by this method has consistent electroactive properties: the uniformly coated layer may exhibit good adhesion between the conductive core fiber and the organic piezoelectric coating layer. This facilitates a high reliability production of the textile device by the braiding and polarizing process without any short-circuit problems.

-A diversified structure of 2D or 3D that can be produced for textile device manufacturing: good adhesion between layers contributes to challenge diversified braiding techniques.

A wearable device with low acoustic impedance can be manufactured.

Claims

1. A method (1) for manufacturing a fluoropolymer coated wire comprising:

-a step (2) of providing a solution of the metal wire and at least one fluoropolymer in a solvent, wherein the fluoropolymer has a proportion of less than 10% by weight and 1% by weight or more, preferably a proportion of 9% by weight or less and 3% by weight or more, and most preferably a proportion of 8% by weight or less and 5% by weight or more, relative to the total weight of the solution;

-a step (3) of dip-coating the metal wire in a first solution of the fluoropolymer to deposit a first layer of the solution of the fluoropolymer at the surface of the metal wire;

-a step (4) of drying to evaporate the solvent from the deposited first layer and form a first layer of the fluoropolymer at the surface of the metal wire; and, a step of, in the first embodiment,

-Optionally one or more subsequent steps of dip coating (5) and drying (5), respectively, to add further layers of the fluoropolymer, the ratio of solvent and fluoropolymer in solution for the subsequent steps of dip coating being independently selected.

2. A process as claimed in claim 1, wherein the fluoropolymer is a copolymer comprising at least 80 mole% of units derived from vinylidene fluoride (VDF) and from trifluoroethylene (TrFE),

3. A method as in claim 2, wherein the fluoropolymer is a P (VDF-TrFE-X) terpolymer consisting of:

-50 to 80 mole% of units obtained from VDF;

15 to 40 mole% of units derived from TrFE, and

-1 To 15 mole% of units obtained from a third monomer X, preferably selected from the list:

tetrafluoroethylene, hexafluoroethylene, trifluoropropene, tetrafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene;

and most preferably the third monomer is chlorotrifluoroethylene or chlorotrifluoropropene.

4. A process as claimed in claim 2 wherein the fluoropolymer is a copolymer consisting essentially of or consisting of units derived from VDF and TrFE, wherein the proportion of units derived from TrFE ranges from 15 to 55 mole%, preferably from 16 to 45 mole%, more preferably from 17 to 35 mole%, and most preferably from 18 to 28 mole% relative to the sum of units derived from VDF and TrFE.

5. A method as claimed in any one of the preceding claims, wherein the solvent is selected from the list of:

Amides, such as dimethylformamide and dimethylacetamide,

-A solvent of dimethyl sulfoxide and a solvent of dimethyl sulfoxide,

Furan, in particular tetrahydrofuran,

The presence of carbonates, in particular dimethyl carbonate,

Phosphate esters, in particular triethyl phosphate,

-And mixtures thereof

6. The method as set forth in claim 5, wherein the solvent is selected from the list of:

Methyl ethyl ketone, cyclopentanone, dimethyl sulfoxide, and mixtures thereof.

7. The method of any one of the preceding claims, wherein the solution is free of any surfactant and/or free of any adhesion promoter.

8. A method as claimed in any one of the preceding claims wherein the solution consists of the fluoropolymer and the solvent.

9. A method as claimed in any one of the preceding claims, comprising 1 to 100, preferably 3 to 50, and more preferably 5 to 20, subsequent steps of dip coating and drying.

10. A method as claimed in any one of the preceding claims, wherein the average thickness of the fluoropolymer coating at the surface of the metal wire is 0.1 to 100 microns, preferably 0.5 to 50 microns, and more preferably 1 to 40 microns.

11. A wire obtainable by the method of any one of claims 1-10.

12. A piezoelectric textile comprising at least one wire obtained by the method of any one of claims 1-10.